CRISTAL is an undulator-based multi-technique diffraction beamline, dedicated to studies of the structural properties of condensed matter, on different length and time scales, possibly in non-ambient conditions. All the standard techniques for structural analysis on single crystals and powders are proposed, as well as more advances techniques like coherent diffraction imaging and time-resolved diffraction in a pump-probe scheme.

The beamline consists of 4 radio-protected hutches and one laser hutch, a control room and a living space.

Figure 1: CRISTAL schematic 3D view.

Figure 2: CRISTAL synoptic.

X-ray Source

CRISTAL’s source is an in-vacuum U20 undulator (98 periods of 20 mm) offering to choose the X-ray energy between 5 keV and 30 keV with a minimum gap of 5.5 mm.

Monochromator

The monochromator is a Si(111)-Double Crystal Monochromator (DCM) with possible sagittal (horizontal) focusing (i.e. bending of the second crystal).
The first crystal is cooled down by a liquid nitrogen closed loop circuit (Cryotherm company). The tuning of the monochromator is ensured by a piezo-actuator, controlled by a feed-back loop on the intensity or the position of the beam measured downstream.

Mirrors

The mirror system consists of two horizontal 300 mm long Si mirrors (SESO), placed in a dedicated hutch. The first one is bendable. These mirrors are coated by Rh and Pt tracks (harmonic rejection in the whole energy range). Slope errors are about 0.40 µrad for both mirrors. The minimum beam FWHM has been measured to be 27 µm @ 8 keV at the sample position at 6-circle diffractometer center.

2-Circle diffractometer

Most of the powder diffraction experiments are performed on the 2-circle diffractometer. This dedicated instrument was initially optimized to record high angular resolution diagrams for ab initio structure determination, microstructure analysis or to study phase transitions, thanks to its multi-analysers detector (21-Si(111) crystals). A complete powder diagram up to 100° 2θ can be measured in less than 1h.

The curve below gives the instrumental resolution determined from the full width at half maximum of the Bragg peaks extracted from the powder diagram of a LaB6 sample (NIST-SRM660, cubic Pm3m) at 25 keV.

Instrument Résolution Function (IRF) at 25.55 keV as a function of the 2theta diffraction angle.

Recently (2018), a curved pixel detector (9x Dectris Mythen II modules, positioned on a cylinder with a radius of 720 mm) was added to the detection circle, providing a 50° 2θ coverage with small gaps (0.5°) or a 25° coverage with no gaps when a non-symmetrically position with respect to the incident beam direction is adopted. A good angular resolution is kept (<0.02° 2θ) is kept. Due to its very short readout time (2ms), a complete powder diagram (up to 2θ = 50°) can be acquired within a few seconds if the detector movements are optimized.

For PDF experiments, to achieve high Q values (> 25Å-1), the highest energies available are used (28 to 30 keV), combined to a scan of the detector position to at least 120° 2θ. Using the Mythen detector, a complete diagram for pdf analysis purposes can be obtained within 1 hour (6 h with the multi-analysers).

4-Circle diffractometer

View of the 4-circle diffractometer equipped with a gas streamer (CryoIndustries of America) to cool the sample. Insert: axes names.

The 4-circle diffractometer allows an easy, fast and precise data collection on single crystals in different sample environments. The instrument specially built for the beamline has resulted from the association of two companies each well known in their area: Newport (Microcontrol) for the goniometer part and Rigaku Oxford Diffraction) for the detector and data analysis software.
The data are measured using the oscillation method: for each image acquisition, the diffraction signal is measured while the sample is rotated at constant speed over a small angular range (typically 1°).

very small Sphere Of Confusion* to be able to study micro-crystals (Ø < 10 µm),

data acquisition/analysis software package standard and familiar to most users.

*the Sphere of Confusion (SoC) is the largest dimension of the spherical volume described by the sample during the motion of all the axes.

6-Circle diffractometer

Newport 6-circle diffractometer, in a vertical position.

The 6-circle diffractometer is the most versatile instrument of the beamline.

It consists of four rotation axes for the sample stage (Mu, Komega, Kappa and Kphi) and two rotation axis for the detector stage (Delta and Gamma). 3 additionnal translations are supported by the kphi rotation axis to accurately position the sample onto the center of the diffractometer.

The measured angular accuracy of all axes are better than 0.001°. The sphere of confusion is better than 60 µm.

An analyser (beam polarisation analysis) can be mounted on the detector arm (as shown on the picture).

Detectors

The 2-circle and 4-circle diffractometers have their own detection system(s). Below is a list of other detectors used at CRISTAL, either belonging to the beamline or to the detector pool. The possibility to use a particular detector on a given instrument is symbolized by the colored icons.

Point detectors

YAP, CeBr3 scintillators CRISTAL : point detectors used for high resolution diffraction

Purchased in common with SIXS and GALAXIES
Will be available in Novembre 2012.

Will be used:
• Coherent diffraction and ptychography.

Pression

Ambient temperature pressure setup

The sample is a Membrane Diamond Anvil Cell (MDAC), on the Phi stage of the 6-Circle diffractometer. The detector is the MAR345. A laser, located at 90° of the X-ray beam, can be approached to the 90° rotated MDAC, in order to measure the fluorescence of ruby crystals in the DAC. This in situ pressure measurement, allows one to change the pressure without removing the MDAC.

Low temperature pressure setup

The MDAC is located in a specially designed liquid Helium flow cryostat (Tmin=14 K and soon 5 K). Equipped with Kapton windows. The detector is a Rayonix CCD camera. The in situ pressure measurement is the same than the ambient pressure one. The picture shows a pressure measurement, with the laser on.

This cooling system has been designed to fit the 6-circle diffractometer in order to allow many diffraction configurations. Beamline usage shows that the limitation mainly comes from the He-outlet. This cryostat is used for the diffraction experiments which are not sensitive to vibrations.
Tmin = 6 K.

ARS HELITRAN liquid helium flow cryostat
placed on the 6-circle diffractometer with the coherent diffraction settings. This cryostat, which has angstrom level vibrations, is well suited for such experiments. Contrarily to the previous displex system, this cryostat is not free to move in any orientation, and should work near the vertical position as shown on the picture.
Tmin = 4 K

Gas blowers

Hot gas blower (Cyberstar) for powder and single crystals.

Temperature range 20-900 °C

Gas streamer cooler (N2/He)
From Cryo Industries of America. Lowest temperature with N2 : 80 K and with He: 30 K. In order to avoid ice formation on the sample, a heated goniometer head is used.

Powder diffraction at low temperature using a gas streamer and a special enclosure. Temperature range: 60K - 300K